Add `camelcase` rule to eslint

Fix camelcase eslint errors in app.ts

GitLab: #2
Change-Id: I083c3f137845298b01dff8c82b2490ab673e589b
diff --git a/.eslintrc.cjs b/.eslintrc.cjs
index 537f3e4..16644b3 100644
--- a/.eslintrc.cjs
+++ b/.eslintrc.cjs
@@ -77,6 +77,7 @@
     '@typescript-eslint/no-empty-function': 'off',
     '@typescript-eslint/no-explicit-any': 'off',
     '@typescript-eslint/no-unused-vars': 'off',
+    camelcase: 'error',
     eqeqeq: ['warn', 'smart'],
     'header/header': header,
     'no-constant-condition': ['error', { checkLoops: false }],
diff --git a/app.ts b/app.ts
index b86cb64..d8dd1dd 100644
--- a/app.ts
+++ b/app.ts
@@ -18,8 +18,8 @@
 'use strict';
 
 import dotenv from 'dotenv';
-const node_env = process.env.NODE_ENV || 'development';
-dotenv.config({ path: `.env.${node_env}` });
+const nodeEnv = process.env.NODE_ENV || 'development';
+dotenv.config({ path: `.env.${nodeEnv}` });
 
 import cors from 'cors';
 import express, { NextFunction, Request, Response } from 'express';
@@ -115,14 +115,14 @@
 
 const createServer = async (appConfig: AppConfig) => {
   const app = express();
-  console.log(`Loading server for ${node_env} with config:`);
+  console.log(`Loading server for ${nodeEnv} with config:`);
   console.log(appConfig);
 
   const corsOptions = {
     origin: 'http://127.0.0.1:3000',
   };
 
-  if (node_env === 'development') {
+  if (nodeEnv === 'development') {
     const webpack = await import('webpack');
     const webpackDev = await import('webpack-dev-middleware');
     const webpackHot = await import('webpack-hot-middleware');
@@ -142,9 +142,9 @@
     */
   app.disable('x-powered-by');
 
-  const secret_key = process.env.SECRET_KEY_BASE;
+  const secretKey = process.env.SECRET_KEY_BASE;
 
-  if (!secret_key) {
+  if (!secretKey) {
     throw new Error('SECRET_KEY_BASE undefined');
   }
 
@@ -156,7 +156,7 @@
       secure: false, //!development,
       maxAge: 2419200000,
     },
-    secret: secret_key,
+    secret: secretKey,
   });
 
   app.use(sessionMiddleware);